Electronic musical instrument



May 8, 1951 F. D. MERRILL, JR

ELECTRONIC MUSICAL INSTRUMENT 3 Sheets-Sheet 1 Filed Nov. 7, 1944INVENTOR. fkmfk/aflMfPe/u JP OUTPl/l' May 8, 1951 F. D. MERRILL, JR

ELECTRONIC MUSICAL INSTRUMENT 5 Sheets-Sheet 2 Filed Nov. 7, 1944 OUTPUTlllll l l y 1951 F. D. MERRILL, JR 2,551,807

ELECTRONIC MUSICAL INSTRUMENT Filed Nov. 7, 1944 3 Sheets-Sheet s Fig 5.z

' 1?.1. I v v v 7 7i 54 1 f i5 k 65 To x-vw ATTORNEY Patented May 8,1951 ELECTRONIC MUSICAL INSTRUMENT Frederic D. Merrill, Jr., Orange, N.J assignor to Radio Corporation of America, a corporation of DelawareApplication November 7, 1944, Serial No. 562,347

4 Claims.

the vibrator motion at different portions of the vibrator.

A primary object of my invention is extension of the timbre range ofmusical instruments of the electronic type.

An additional object of my invention and one resulting from theattainment of the primary object is comparison of vibratory motion atdifferent points on the vibrator.

An advantage of obtaining a greater range or variety of timbre is toincrease the tone expressiveness of the instrument and to simulate to asgreat a degree as possible orchestral timbres. For example, in a pianothe obtaining of a strident timbre presents difliculties which are onlyfully solved by means of my invention. On the other hand by my inventionmore or less strident timbre may be obtained thus extending the range oftimbre obtainable. Other examples will occur to those versed in theelectronic musical art.

For the sake of brevity and clearness and to simplify the description,reference will be made hereinafter to electronic instruments of thestring type. My invention, however, is applicable to any vibrating bodysuch as piano strings, reeds, etc.

The broad concept is as follows. The relative amplitude of each harmonicmotion of the string varies along the string length. For example, thefundamental mode of vibration has a maximum amplitude at a pointhalf-way along the string length. Also along the string length there isa steady progression of points of maximum vibration for a given harmonicand points of minimum amplitude of motion for the same harmonic. Thecharacteristic vibration at any point along the string length may betranslated into corresponding variations of electric current flow bymeans of suitable pickup devices spatially separated from the strings.These may be based on magnetic, capacitative, or other methods. If nowsuch pickups are arranged in opposing relationship as far as thegenerated voltage is concerned, then a new group of timbres may beobtained giving a wider range of tone quality than that from any singlepickup located at any one point along the string length. The use ofreactive pickups in bucking arrangements for frequency modulation ofoscillatory energy is novel and useful. I have disclosed various meansfor obtaining bucking pickup with frequency modulation systems. The likecomponents from the outputs of two difierently effective pickups are cancelled out, leaving a strikingly different timbre from that of theseparate outputs. The pickups may be differentially associated with thevibrating element or may be located in similar relation with respect tothe element and their efiects used differentially.

In describing my invention in detail reference will be made to theattached drawings wherein Fig. 1 illustrates by circuit diagram theessential features of my improved electronic pickup and modifying means.As illustrated this means includes an oscillation generator, a frequencydetermining circuit therefor, a vibratory element and a reactance,comprised in part thereby, variable by motion thereof, for tuning theoscillation generator to various frequencies.

Fig. 2 is a basic diagram illustrating the manner in which the frequencycontrol of the arrangement of Fig. 1 is accomplished.

Fig. 2a is a modification of the arrangement of Fig. 1.

Fig. 2b is a modification of the arrangement of Fig. 2a.

Figs. 3, 4, and 5 each illustrate modified embodiments of my system asillustrated in the prior figures. In Fig. 3 the pickup elements arearranged on the same side of the vibratory element, whereas in Fig. 1they are arranged on opposite sides.

Fig. 4 is a basic diagram of the arrangement of Fig. 3.

In Fig. 5 magnetic pickup means is used, whereas capacitive pickup meansare used in the prior figures.

Figs. 5a and 5?) illustrate details of means for adjusting the pickupelements of Fig. 5 relative to the strings of an instrument such as apiano.

Fig. 3a illustrates a modification of the arrangement of Fig. 3.

Referring to Fig. 1, a metal string I is stretched between two bridgesby means of the tuning pins 2. The capacity variations between a metalstring and spatially separated electrodes 8 and 4 are used to frequencymodulate a super-audible generated voltage. The electrodes 4 and 8 maybe machine screws mounted in supports (not shown) for adjustment towardand from the string I. For electrostatic shielding and con venience ofconstruction the strings (of which but one is shown) are grounded. Thetwo capacity pickups may be at different positions along the string buton opposite sides of the string. There is capacity between the stringand each metal adjustably positioned machine screw 4, 8. The capacityvaries as the string vibrates. Feedback from L2 in plate circuit of tubeto the grid coil LI causes the tube 5 to oscillate. This oscillation isassisted by the grid leak condenser RI, C3, as well as the necessary D.C. return path from the grid of the tube through R2. Fig. 2 shows bysimplified connections the capacity varying part of Fig. 1. The topplate of C4 represents the pickup electrode 4. The top plate of C8represents the pickup electrode 8. The variable condensers Cl and C2determine the magnitude of the effect of each pickup on the resonantfrequency of the oscillating circuit. -As the string moves towardspickup i, the capacity C4 increases, tending to lower the resonantfrequency. The string I, however, is simultaneously receding from pickup8 so that C8 diminishes, tending to raise the generated frequency. Theinstantaneous capacity in the resonant circuit is therefore thedifference between C8 and Cd. The like capacity changes thereforeneutralize one another, leaving only the dissimilar capacity variations.The amount of bucking is of course predicated upon the adjustments of C2and CI. C2 and Cl also determine the maximum frequency swing of thecarrier frequency. L2 merely picks up the frequency modulated voltageand supplies it to a utilization circuit such as for example an F. M.receiver. C5 adjusts the overall quiescent frequency of the oscillator.

In Fig. 2a I have shown an alternative method by means of which theresistance R2, indicated as R5 in Fig. 2, is eliminated. In thisarrangement as in the prior embodiment C6 and C8 are the variables andinspection of this figure will show that when C4 is increased it willtend to lower the frequency of the operation of the generator, since itis in shunt to the tank circuit including Ll. At the same time thereactance of C8 decreases and since this condenser is in shunt to thetank circuit it will have a tendency to increase the frequency ofoperation thereof so that the like variable components oppose andcancel, leaving the resultant capacitive effect representing primarilyharmonic modes of vibration of the string which are unlike at the twopickup points.

While in Figs. 1, 2, and 2a I have shown a single pair of pickupelements 4 and 8 adjacent the vibratory element, it will be understoodthat additional pairs 5', 8' and 4 and 8" may be added and connected inparallel with the reactive pickups 4 and 8, as illustrated in Fig. 2b.The number of pickups is of course limited by the total fixed reactanceplaced on the tank circuit.

Moreover, it will be understood that in these embodiments and in theones which follow, pickup elements associated with a large number ofstrings such as in a piano may be associated with one oscillator orthere may be an oscillator for groups of strings, for example, for eachoctave.

which my invention is applied is such that application of the pickups onopposite sides of the string is difiicult mechanically, the pickupelectrodes may all be placed on the same side of the string. Thismodification may be applied to the arrangements of Figures 1, 2, and 2aprovided certain changes are made. The changes necessary will be clearto one who understands the arrangement shown in Fig. 3. In thearrangement of Fig. 3 pickups on the same side of the string are used. Apiano is an example of an instrument where it may be desirable to havepickups on the same side of the vibratory element. In this instrumentlocation of the pickups on opposite sides of the string is notconvenient mechanicall and certainly would be more expensive than anarrangement where the pickups are on the same side of the string. Fig. 3shows a method for avoiding this situation. The associated varyingcapacity elements are drawn more clearly in Fig. 4. The feature of thiscircuit is the L4, Cl, pickup capacity from the pickup 4 to ground. Thisportion of the circuit acts something like a short circuiting inductanceto Ll, to which inductance L4 is coupled and thus will affect theoscillator frequency. The couplin between LI and L l should be primarilymagnetic, not electrostatic, and electrostatic shielding S between thetwo coils may sometimes be necessary to insure all mag netic coupling.An explanation of the functioning of the circuit is as follows. Supposethe metal string I approaches the two pickups 4 and 8. C4 and C8represent the capacity between the string and electrodes 4 and 8respectively. If C4, the capacity of string to pickup electrode,increases, this diminishes the impedance across L4 and tends to decreasethe inductance of the Li circuit and thus raises the oscillatorfrequency. However, as the string is approaching both pickupssimultaneously, C8 also increases, and tends to lower the oscillatorfrequency. The difference between the relative magnitudes of these twoeffects will determine the actual oscillator frequency. Similar capacitychanges cancel out, leaving only the unlike portions. Cl, C2, C9determine the individual effects of each pickup capacity change on theoscillator frequency. C5 gives an overall control of the oscillatorfrequency.

Fig. 5 shows a method for obtaining magnetic pickup bucking action,again employing frequency modulation as the energy source beingmodulated. In this case the vibrating string I should be of iron orsteel. The electrostatic shielding is shown at 29 by the dash line. Themagnetic pickup coils Lit and LIZ are individually adjustable inseparation from the string just as in the case of the other figures. Thecores may be air, soft iron, or a permanent magnet. Li, L2 here as inthe prior figure constitutes the oscillating circuit whose frequencywill be varied in accordance with the variations of inductance of Lil]and LIZ. The inductance of Llfi and LIZ will vary because the approachof the steel string will change the flux linkages set up by the winding(the oscillator current flows in the magnetic pick-up coil). As thestring l nears the two pickups, both Ll El and LE2 increase ininductance. The inductance of M2 is additive to (in series with) that ofLI, so the oscillator frequency should tend to diminish. Ll!) is in acircuit parallel with Li so the total inductance should diminish andtherefore the oscillator frequency rise. These are two opposing effectsso like vibration components of the string tend to be cancelled out,leaving only the unlike components. R3 and R4 ar rheostats to vary theeffect of LIB and LIZ respectively on the oscillator frequency. C5 againadjusts the overall oscillator frequency to any desired value.

Adjustment of the pickup elements of Fig. 5 with respect to the stringmay be accomplished in various ways. For example, as illustrated inFigs. 5a and 5b the magnetic pickup coil winding 30 (LID and LIZ Fig. 5)may be associated with a magnetic pole 5 adjustably mounted in a support34 for movement toward and away from the string I. Set screws 3| and 32having slotted heads may be passed through the support 34 and bear onthe pole piece 5 to retain the same at the desired distance from thestring I. In some cases it is preferable that the set screws 3| and 32have hexagon heads (recessed) so that they may be conveniently turned bya hexagon wrench passed through the strings and pivoted in a planebetween strings.

In all six circuits described hereinbefore and in Fig. 3a describedhereinafter there is assumed to be mutual induction between all coils.The oscillator frequency should be above the range of hearing. Theeffect of minute capacity or inductance changes on the frequency of anoscillating circuit Will in general increase with the frequency. Thismay recommend the use of a high oscillator frequency. Also spuriousmechanical vibration (of electrical circuit parts) should be eliminatedto prevent introduction of spurious signals.

A separate oscillator for each vibrator is not necessary for the pickupsor groups thereof may all be placed in parallel with each other. This isillustrated in Fig. 3a wherein additional strings I and l" haveassociated therewith pickups 4a and 8a and 4b and 8b. This arrangementotherwise may be as illustrated in any of the prior figures. Asillustrated, Fig. 3a is basically as illustrated in Fig. 3 and operatesin the same manner in which the arrangement of Fig. 3 operates.

In my improved method and means, then, the effects of the fundamentaland lower harmonics cancel to a greater extent than the higherharmonies, the nodes and antinodes of which are closer together. Thisthen stresses and enhances the higher harmonics. If the pickups arespaced farther apart, stressing of the higher harmonics may be reducedby selection of the pickup points. As the separation between the pointsof pickup is increased the difference between the opposing effects atthe fundamental mode of operation is increased. The higher the order ofthe harmonic the shorter the distance between the nodes and antinodes,therefore bringing the pickups toward each other causes a more completecancellation of the fundamentals, leaving predominantly variations ofthe higher harmonic modes of operation. Particularly is this so when thepickups are near the ends of the vibrating string.

What is claimed is:

1. In an electronic instrument, in combination, an oscillation generatorcomprising an electron discharge tube having electrodes coupled in acircuit including an inductance between two of the tube electrodes, asecond inductance coupled to said first inductance, a conductivevibratory element having one terminal connected to one terminal of eachof said inductances, a pair of pickups adjacent said element each toprovide a varying reactance as said element vibrates, a connection toone pickup for putting one of the said reactances in shunt to one ofsaid inductances, a connection to the other pickup for putting the otherof said reactances in shunt to the other of said inductances, and anoutput circuit coupled to said generator.

2. In an oscillation generator, an electron discharge device havingelectrodes regeneratively coupled in an oscillation generating circuitincluding a reactance, a conductiv vibratory element having one terminalcoupled to said reactance, a pair of pick up devices spaced along oneside of said vibratory element to provide reactance variations ofdifferent magnitudes as said element vibrates, and couplings betweensaid pick up devices and said reactance for adding said reactancevariations differentially to the reactance of said circuit.

3. In an oscillation generator, an electron discharge device havingelectrodes regeneratively coupled in an oscillation generating circuitincluding an inductance, a conductive vibratory element having oneterminal coupled to said inductance, a pair of pick up devices spacedalong one side of said vibratory element to provide capacity variationsof different magnitudes as said element vibrates, and couplings betweensaid pick up devices and said inductance for adding said capacityvariations to the inductance of said circuit in opposed sense.

4. In an oscillation generator, an electron discharge device havingelectrodes regeneratively coupled in an oscillation generating circuitincluding an inductance connected between two of the electrodes of saiddevice, a conductive vibratory element having one terminal coupled tosaid inductance, a pair of pickup devices spaced along one side of saidvibratory element to provide inductance variations of differentmagnitudes as said element vibrates, one of said pickup devicescomprising a magnet having a core in inductive relation to said elementand having a winding coupled in series with said inductance and theother of said pickup devices comprising a magnet having a core ininductive relation to said element and having a winding coupled in shuntto said inductance, whereby said inductance variations are addeddifferential- 1y to the inductance of said circuit, and an outputcircuit coupled to said oscillation generating circuit.

FREDERIC D. MERRILL, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,027,074 Miessner Jan. 7, 19362,220,350 Purington Nov. 5, 1940 2,318,936 Fisher May 11, 1943 2,323,231Merrill June 29, 1943 2,413,062 Miessner Dec. 24, 1946 2,444,218Carnahan June 29. 1948

